How to reduce oil carryover in compressors in the refrigeration industry

The majority of compressors used in refrigeration systems are oil injected. Sometimes a compressor unit shows higher oil consumption than calculated.

Over the last five years we have investigated the most common reasons related to oil carryover. During our field investigations we noted interesting findings relating to oil carryover. Even older compressor installations started to show more oil consumption than they had previously demonstrated.

Top 3 reasons for oil consumption:

  • The oil and refrigerant mixture is entering the oil recovery system outside the ideal separation area. The adhesion is too strong between lubrication oil and refrigerant. The time in the oil separator is too short to reach 100% separation.
  • The amount of oil/refrigerant flow is too big to handle by the oil separator. By VSD application the flow is variable over a big user area.
  • In the production process, because oil is based on different viscosity the oil separator can be partly blocked and forced to work outside design limits.

 

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The relationship between the main systems of a compressor unit:

 

 

 

 

 

 

 

 

 

 

 

How to reduce the oil carryover of your compressor system:

  • Find the ideal separation temperature between your refrigerant and the used oil. Enter the oil recovery system with this temperature. The entry temperature of the oil recovery system is based on the heat generated by the compressor used.  Some refrigerants generate temperature under the ideal separation temperature; this must be compensated.
  • Calculate your ideal oil flow and used compensation regulation if needed. In most cases corrections in entry temperatures can be used to correct the flow. Doing this after separation can always be used as second option, if the existing oil compressor is limited in size.
  • By using oil with a different viscosity in combination with an oil separator that is designed in two stages (last stage with oil separator elements). The last stage can block the heaviest part and the elements will go outside the design limits. We can only use a three phase oil separator with a mixing phase to enter the last stage. This type of separator can also be used as the central after oil separator in the refrigeration system. The capture oil can be sent to the compressor with the lowest oil level.


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